Such a bending device is known from the Patent Abstract of Japan No. 06170449.
This known bending device is used for bending composite pipes, wherein the presence of the bending mandrels in both channels of the pipe prevents the outer wall of the respective channel for bending from being distorted inward during the bending. The presence of the bending mandrel prevents the outer wall of the channel being subjected to bending from displacing inward.
On the inside the effect is the reverse; the material is buckled so that it tends to displace inward as a result of the excess of material.
These problems are obviated by the use of a bending mandrel, in particular a pivotable bending mandrel.
The bending mandrel known from JP 06110449 comprises cylindrial elements. The axes of the elements extend perpendicular to the bending radius and to the axial direction of the pipe. This implies that only on discrete: points the pipe walls are supported during bending, so that the pipe walls will be buckled.